[OpenWrt-Devel] [RFC PATCH] build: re-enable parallelism for mksquashfs

[Felix Fietkau]

On 2018-11-08 02:20, Daniel Santos wrote:
> On 11/07/2018 01:52 PM, Felix Fietkau wrote:
>> On 2018-11-05 00:19, Daniel Santos wrote:
>>> This was disabled by commit dcd0e4a6727611f03eb3d3a75f073235f5f1229c due
>>> to a threading bug back in 2009.  The specifics of the bug are not given
>>> in the commit message and squashfs-tools has had several updates to it's
>>> parallelism since this time.  There are currently no open issues related
>>> to parallelism in their issue tracker:
>>> https://github.com/plougher/squashfs-tools/issues
>>>
>>> It now "works for me" with 16 threads, and while this is a terrible test
>>> for a race condition I still propose we remove this work-around
>>> unless and until we have specific knowledge of a current bug.
>>>
>>> Signed-off-by: Daniel Santos <daniel.santos at pobox.com>
>> Are the images still reproducible after that change?
>> If I remember correctly, threading would break that.
> Hello.  I'm not sure what you mean by the images being reproducible. 
> I've been building with TARGET_ROOTFS_SQUASHFS=y and
> TARGET_ROOTFS_SQUASHFS=256 for a few weeks now without any problem.  I'm
> presuming they've fixed it, but I didn't see specific mention of this
> bug in their github issue tracker.  They may have discussed it elsewhere
> prior to porting to github.
Reproducible as in https://reproducible-builds.org/
You're supposed to be able to generate the binary-identical rootfs image
on different machines, as long as you're using the same version and the
same configuration.
From my understanding, using multiple threads for the squashfs build can
make the order in which data appears in the filesystem image
non-deterministic.

- Felix


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